Every year, the world faces huge losses in lives and property due to residential and commercial fires caused by, electrical wiring. Human lives can be lost due to high temperature flames, toxic smoke and gas that are generated from the flammable insulation materials used in wire and cable during fire.
The current population uses many equipments and gadgets that contain several wires and cables. Most wires and cables are fabricated from plastic materials that are readily flammable. Moreover, modern living involves heavy use of electric equipment containing wires and communication systems made of cables. These conditions further increase the loss of lives and properties due to bad insulation of a wire or a cable resulting in an electrical fire. Smoke and toxic fumes from poor insulation materials in wires and cables can cause irreparable health damage.
Wire and cable insulations are required to meet not only the electrical properties but also the mechanical properties. Polyethylene and polyvinylchloride compounds are some of the best materials suitable for wire and cable insulations because of their excellent electrical and mechanical properties. However, these materials have poor flame retardancy and generate toxic gases during a fire.
Polyethylene, for example, is easily flammable and generates less toxic gases during the burning process. On the other hand, Polyvinylchloride compounds generate a lot of toxic gases during a fire, even though it has acceptable flame retardancy. Currently, clean flame retardant materials are made from special formulations. These special formulations are made of halogen and toxicity free chemicals. Clean flame retardant materials mainly consist of matrix polymers that do not contain halogen, main flame retardants, secondary flame retardants, intumescent flame retardants, processing aids and antioxidants. (Mans V et al. 1998, Rai M et al. 1998, Wei P et al. 2006 and Luciana R et al. 2005). The resultant mixture has very poor mechanical properties.
The other biggest problem with commercially clean material is that they have unstable mechanical properties, even though they possess high flame retardancy, due to high filler loadings. Clean flame retardant materials contain relatively high content of inorganic materials as flame retardants. In general, high levels of flame retardants are necessary to achieve commercially acceptable flame retardancy levels for wires and cables. However, high levels of flame retardants may lead to deterioration of mechanical properties. Insulation and jacket materials for wire and cable should meet appropriate standards for tensile strength, elongation at break, thermal resistance and flame retardancy for an extended application time. Enhanced cable insulations must also meet IEC 60502, BS 6724 and BS 7655 standards specific for thermoplastic compound requirements.
EVA (ethylene vinyl acetate), EVA/LDPE (low density polyethylene)(or LLDPE (linear LDPE), ethylene alpha olefin or ethylene ethyl acrylate are widely used as matrix polymer because of their high flame retardant load ability and increased flame retardancy. Main flame retardants mostly comprise of inorganic materials, such as, aluminum trihydroixide (ATH), magnesium hydroxide (MH) and huntite hydromagnesite (HH). They exhibit high decomposition temperature and have the ability to suppress smoke as clean flame retardant materials. However, more than 50% w/w loading is required to achieve the target flame retardancy. Unfortunately, such high contents of flame retardants can lead to interfacial problems between matrix polymer and flame retardants and then, can negatively affect the mechanical properties.
Various studies were performed to improve mechanical properties and flame retardancy by using organic encapsulated flame retardants (Chang et al. 2006, Du L et al. 2006, Liu Y et al. 2006), and synergistic effect of hydrotalcite with two flame retardants and organo-modified montmorillonite (Laoutid F et al. 2006, Ma H et al. 2006).
Organic encapsulated flame retardants can enhance the interfacial adhesion with matrix polymers and lead to improved dispersion compared to non-encapsulated flame retardants. Hydrotalcite composites increase flame retardancy by releasing more gas compared to other flame retardants during burning. In addition, partial substitution of flame retardants by organo-modified montmorillonite improves the burning properties. All these result only in improved flame retardancy.
Specification standards for wire and cable insulation composition require high flame retardancy and superior mechanical properties. For example, the minimum required tensile strength is 8.8 MPa and minimum elongation at break is 125% based on IEC 60502, BS 6724 and BS 7655 standards for thermoplastic compounds. Moreover, additional treatment of flame retardants or mixing with special chemicals increase cost performance of final products. There is a need to obtain a wire and cable insulation material that contains a clean flame retardant material, has superior mechanical properties and high flame retardancy. Without meeting these important properties, the clean flame retardant materials are not suitable for wire and cable insulation purposes.